In the past, much effort has been devoted to the development of railroad tie fastening assemblies. In the nearly two centuries since railroads began to shrink the vast expanses which separate us, rail systems have evolved from the crude forgings and substantially raw timber ties, which the limited range of technologies available at the time could produce, to more elaborate systems, including chemically treated wooden ties and, in more recent times, concrete railroad ties. The desirable qualities of railroad rail fastening assemblies include reliability, wear and abrasion resistance, cushioning ability, electrical insulation of the rail, ease of installation, and economy.
In recent years, the trend has been toward railways which have their rails set on concrete rather than the older wooden ties. Standing alone, however, these concrete ties lack some of the advantageous qualities of the traditional wooden ties which they are replacing, such as vibration dampening characteristics. In order to improve the characteristics of concrete rail tie rail support systems, fastening systems utilizing rubber pads have been developed. The rubber pads have been found to be useful in damping rail vibrations, and electrically insulating the rail from the concrete tie.
For example U.S. Pat. No. 3,581,990 Kirik, discloses a rail mounting assembly for use in connection with concrete railroad ties. In the assembly disclosed in this patent, a rubber tie pad having electrical insulating, sound deadening, and vibration dampening properties is positioned between the rail and the concrete tie. This allows the rubber tie pad to electrically insulate the rail from the concrete tie, reduce rail slippage, and dampen rail vibrations and noise.
While the addition of a rubber tie pad improved some of the drawbacks associated with concrete ties, at least one new problem was created. Traditionally, a locomotive is used to apply a silica sand to a rail for the purpose of improving traction in areas of the track where slippage of the wheels can occur. The most common place for the application of sand to the rail is on a curve or on an incline.
As may be apparent, the use of sand on a rail which is inclined prevents wheel slippage. The need to apply sand to curved sections of railroad track arises because, when a train encounters a curve, the momentum of the train attempts to force the train to continue moving in a straight line. Of course, the rail on the outside of the curve then forces the train to continue along the curve. The use of sand on the curved portion of a rail tends to keep the wheels of the train in engagement with both rails, thus maintaining control and protecting, to some extent, the outside rail from extraordinary stresses. However, the force applied by the train to the rails causes the rubber tie pads to move in relation to the concrete tie. When the sand and moisture seep between the rubber tie pad and the concrete tie, the back and forth movement of the rubber tie pad on the concrete tie causes erosion of the concrete and the rapid deterioration of the rubber tie pad. This results in even more serious slippage and generally increased movement of the rubber tie pad, as well as loss of electrical insulating properties, increased noise and vibration in the rail and a shorter life span for the concrete tie.
In order to improve the resistance of the concrete tie pad to erosion a metal abrasion plate was added to the fastening system. The abrasion plate was placed between the rubber tie pad and the concrete tie. The purpose of the abrasion plate was to protect the rubber tie pad and the concrete from the damaging effects of the sand. The object was to protect the top surface of the concrete railroad tie from any sand or grit which would otherwise be caught between the rubber tie pad and the concrete tie. The expected result would be the concentration of the abrasive effects of the sand on the metal abrasion plate, rather than the concrete tie. Since the plate was made from hardened steel or a similar material, it was expected that little wear would take place on the plate.
In U.S. Pat. No. 4,925,094 Buekett, a concrete railroad tie is disclosed which is characterized by a stainless steel plate cast into the top surface of the railroad tie, having lugs projecting from the plate thereby providing a mechanical connection with the concrete rail tie. A rail pad is then disposed between the plate and the rail. The methods of casting the concrete tie around the plate insures that the plastic plate and the concrete tie match in shape. U.S. Pat. No. 5,110,046 Young, discloses a variation of this idea. In Young, a thin metal plate is placed between a rail pad and concrete rail tie, and the thin metal plate is bonded to the concrete rail tie by use of an epoxy adhesive. However, use of adhesive is not an effective solution, because, in time, sand and moisture become lodged within a void created between the metal plate and the concrete tie, resulting in abrasion and then erosion of the concrete tie.